Hydraulic press



2 Sheets-Sheet l w. P. Mum HYDRAULIC PRESS Filed June 13, 1942 Jul 2,1946.

INVENTOR may 2 Sheets-Sheet 2 Filed June 15, 1942 HNVENTOR V MUER BY I,

ATTOBNE Patented July 2, 1946 HYDRAULIC PRESS William P. Muir,Hampstead, Quebec, Canada, as-

, signor to Dominion Engineering Works Limited,

La'chine, Quebec, Canada Application June 13, 1942, Serial No. 446,994In Canada April 11, 1942 2 Claims. 1

This invention relates to control mechanism for regulating the tonnageor working pressure of a hydraulic press to suit the work being done andto prevent overloading of the work or tooling.

Various methods of regulating the tonnage or working pressure ofhydraulic presses have been proposed and adopted prior to thisinvention. In some cases the discharge of a variable stroke pump whichfeeds the hydraulic press circult is gradually reduced as the workingpressure increases so that, when the desired maximum working pressure isattained, the pump stroke will be Just suflicient to maintain thismaximum pressure against leakage. In other cases the discharge of avariable stroke reversible pump feeding the hydraulic circuit ismaintained substantially constant until the working pressure is'built upto the required maximum value whereupon the pump discharge is stopped orreversed through the agency of a suitable pressure operated pump strokeneutralizing and reversing mechanism. In

other cases pressure-operated controls are pro-, vided for automaticallyoperating the main control valve of the press to transfer the pumpdischarge from the pressing cylinder to the return cylinder or cylinderswhen the working pressure in the pressing cylinder has been built up tothe desiredmaximum value, such operation of the main control'valve alsoserving to establish connections through which pressure fluid isrelieved from the pressing cylinder during the return stroke of thepress.

The foregoing and other methods of "tonnage regulation now practiced areopen to the objection that there is an appreciable time lag between thedevelopment of the desired maximum working pressure in the pressingcylinder and the actual operation of the pump stroke adjustingmechanism, control valve, or other control element relied upon to limitthe rise of the working pressure. If there is any irregularity'in theop-- eration of such pump stroke adjusting mechanism, valve or othercontrol element, th delayed action thereof may permit the workingpressure to exceed the desired maximum value to a sufficient extent tooverload the work or tooling. The method of regulation which involvesthe gradual reduction of the pump discharge as the working pressurincreases is also open to the objection that it slows down the buildingup of the working pressure vto the required maximum value' and thusreduces the operating speed of the press. 7

With the foregoing in mind, an important object of this invention is theprovision of adjustable "tonnage or working pressure regulatingmechanism which functions instantly and independently of the pump-strokecontrolling mechanism and the main control valve to prevent furpump tobe utilized in rapidly building up the working pressure to the requiredmaximum value.

A further object is the provision of a tonnage or working pressureregulating mechanism which, while permitting the full discharge capacityof the feed pump to be utilized in building up the working pressuretothe required maximum value, also includes means whereby the pumpdischarge is automatically reduced after the desired maxi-' mum workingpressure is attained.

A further object is the provision of a "tonnage" or working pressureregulating mechanism including means for effecting either immediate ordelayed operation of the main contro1 valve from a power stroke to areturn stroke position, the arrangement being such that any delay or lagin the operation of said valve to its return stroke 'position has noeffect on the instantaneous operation of said regulating mechanism toprevent .iurther increase of the working pressure when the latter hasbeen built up to the desired maximum value.

A further object is the provision of a tonnage" or working pressureregulating mechanism including means whereby the operation of thereversing valve to effect a return stroke of the press may be delayed topermit the press to dwell on the work at constant pressure for as longas may be desired.

A further object is the provision of a tonnage" or working pressureregulating mechanism which functions automatically in direct and instantresponse to the development of a predetermined working pressure in thepressing cylinder and hydraulic circuit to prevent further rise ofpressure by establishing a relief connection through which the fulldischarged the pump may be bypassed even when the pump is operating atmaximum discharge capacity. This protects both the press and the pumpfrom overloading under any conditions of operation.

A further object is the provision of a "tonnage or ,working pressureregulating mechanism includug a main pressure regulating relief valvethrough which the discharge of the feed pump is by-passed when theworking pressure in the pressing cylinder and hydraulic circuit reachesa predetermined maximum value and a supplementary back pressureregulating relief valve through which the discharge-from the main reliefvalve is passed, said back pressure regulat- I port 40 of a mainpressure regulating relief valve 4| is connected to line 20 by asuitable pipe connection. The discharge port 43 of valve 4| isconnected, by suitable pipe connection 44, to the inlet port 45 of anauxiliary back pressure regulating valve 46, the discharge port 41.0fwhich is connected, by pipe 48, to the previously mentioned relief line25. The valve 4|, pipes 42 and 44, valve 46 and'pipe 48 conjointlyprovide a valve controlled relief line connection between the main fluidline '20 of the pressing cylinder and the relief line 25. As here shown,

valve 4| comprises a casing 49 containing a ver-' tically movable valve50 which is normally closed against its seat 5| by a valve closingspring 52, the compression of which may be varied. by adjustment of thespring compressing nut 53. The valve member 46 also comprises a casing55 containing a valve 56 which is held to its seat 51 by a valve closingspring 58, the compression of which may beregulated by adjustment of thespring compressing nut 60. From'this it will be apparent that the valves4| and 46 may be spring loaded by suitable adjustment of the nuts 53 and60 to open when the fiuid pressure acting to unseat said valves reachesa predetermined maximum value. v

For present purposes it will be assumed that the spring loading of thevalve 4| is adjusted so that this valve will open only when the workingpressure developed in the hydraulic circuit and the pressing cylinder 1during the working stroke of the press reaches a maximum value ofapproximately 2000 lbs. per square inch. The

circuit and the pressing cylinder I. In' this connection it will bereadily understood that the power consumption and the load on the pumpis considerably reduced by reducing the volume of the pump dischargefollowing attainment of opening of this valve in response totheestablishment of such pressure permits the excess discharge of thepump to be passed therethrough and thus prevents further rise ofpressure in the. hydraulic circuit and the pressing cylinder. In thisconnection it may be explained that the valve 4| is preferably made ofsufllcient size to by-pass the full discharge of the pump even when thelatter is working at maximum discharge capacity. The discharge from thevalve 4| passes through the auxiliary back pressure relief valve 46, thespring loading of which is adjusted to maintain an intermediate pressureof, say, 200 lbs. per square inch in the relief line connection 44between the two valves. .As hereinafter described the intermediatepressure thus established in the portion 44 of the pressure regulatingrelief line is utilized to operate the valve II and also the strokeregulating mechanism No of the feed pump i0. It is also available foroperating other controls.

The intermediate pressure established in the portion 44 of the reliefline is transmitted, through pipe 6| and valve 62, we piston 63operating in a cylinder 64 and serves to move the piston downwardlyagainst the resistance of the piston biasing spring 65. The piston 63 isprovided with a stem or rod 66 which, during the downward movement ofthe piston, acts against one of the members of the toggle 39 to operatethe toggle to a collapsed position ermitting the valve member |3 ofvalve II to be shifted to its'return stroke position by'its operatingspring 35. When it is desired to permit the press to .dWell on the workfor a given period subsequent to the development of the desiredpredetermined workin pressure, this is accomplished by operating thevalve 62 to throttle the flow of pressure iluid In this way thecollapsing through the line 6|. of the toggle 39 by the downwardmovement of the valves 4| and 46.

maximum working pressure in the system. The flow of pressure fluidthrough the line 10 is controlled by a suitable regulating valve Whenthe valve element i3 of the main control valve is in its right hand orreturn stroke position the pressure regulating valves 4| and 46 areisolated since, in this position of valve element i3, the fluid line 20is connected to the exhaust line 25. In the return stroke position ofvalve element i3, the intermediate pressure in pipe connections 44, 6|and i0 is relieved via bleed valve l2, pipe 48 and exhaust line 25.

In the foregoing arrangement the discharge from the-main pressureregulating valve 4| is so regulated by the action of the auxiliary backpressure regulating valve 46 that the desired intermediate pressure inthe portion of the relief line between the two relief valves ismaintained constant from the moment the valve 4| opens until the pressplaten 5 is operated on its return stroke. Since this intermediatepressure is maintained practically constant irrespective of the volumeof discharge through the valves 4| and 46 it provides an ideal source ofhydraulic energy for operating the main control valve and the pumpstroke adjusting mechanism Ma.

It is important to note, at this point. that when the desired maximumworking pressure is built up in the hydraulic circuit and the pressingcylinder 7, the valve 4| opens instantly to .prevent further rise ofthis pressure. It will thus be seen that a very close regulation of themaximum working pressure developed in the system may be obtained byappropriate adjustment of the spring loading of valve 4| and that thisregulation is not aileoted by any time lag in the operation of the maincontrol valve i to its return stroke position nor by any time lag in theoperation of the pump stroke adjusting mechanism i011. Consequently, ifthe valves 4| and 46 are made of such size as to be capable ofdischarging the full capacity of the pump, it is possible to delay theoperation of the main valve II to its return stroke position so as topermit the press to dwell on the Work at constant pressure for as longasmay be desired. During such dwell periods the by-passing of the fullpump discharge through the valves 4| and 48 prevents overloading of boththe press and the I pump.

Another advantage of the arrangement described herein is that themaximum working pressure, as determined by adjustment of the valve 4|,remains constant irrespective of the setting of the valve 46 or the rateof the flow through The utilization of the intermediate pressureestablished between the valves 4| and 46 for reducing the pump dischargemakes it possible to economize power and to prolong the life of the pumpwhen operating at long pressure dwells.

Fig. 2 shows another embodiment of the invention in which the stem ofthe main control pressed air will ,7 air through an "f'v'iouslymentioned air lines" and 9|. The openin: of valve 88 permits compressedair to flow to 7 valve [3 is connected to an operating piston 15 workingin an air cylinder 16. The operation of piston 15 is controlled by theaction. of a pilot valve 11 working in a pilot valve casing '18 to whichair under pressure is delivered through a main air line 19. when thepilot valve is in the position shown in Fig. 2 air under pressure isdelivered to the right hand end ofcylinder 15 through pilot valve port.88, pilot valve casing port 8!, and line 82 the air previously suppliedto the right hand end of air cylinder it being exhausted through line 83and a suitable exhaust connection 84 provided in the pilot valve 11. Theair thus applied to the right hand end of cylinder 18 acts against thepiston lb to operate the main control valve 13 to the power strokeposition shown in Fig. 2. When the pilot valve ll is shifted to the leftthe line 83 is connected to the main supply line 19 through the pilotvalve port at so that air under pressure is now supplied to the lefthand end ofcylinder l6 to operate the piston 15 and the main controlvalve element iii to a return stroke position. During this latteroperation of the piston 15 the air previously supplied to the right handend of cylinder 16 is exhausted through line 82 and an exhaust port 85provided in the pilot valve 11.

The pilot valve 'Il may be operated manually through the agency ofsuitable normally closed push button valves 88 and 89. As here shown theinlet ports of these push button valves are connected in parallel witheach other to the main air supply line 19 through the agency of a branchconnection 80. The outlet port of valve 88 is connected to the left handend of pilot valve cylinder I8 by a fluid line 9| while the outlet portof push button valve 89 is connected by pipe line 92 to the right handend of the pilot valve cylinder 18. From this description it will beapparent that when push button valve 88 is opened against the resistanceof its valve closing spring 880:. comof the pilot valve 11 to force thepilot valve to the right. Similarly, the opening of the push buttonvalve 88 against spring 89a causes compressed air ot be supplied to theright hand end of-the pilot valve cylinder 16 to force left. V

In the arrangement shoviir'iin Fig. 2 the intermediate pressureestablished in the section ll of the work-pressure regulating reliefline controlled by valves H and 46 is utilized to effect automaticoperation ofthe pilot valve 11 in the direction necessary to operate themain control valve 13 to its return stroke position. Inthis connectionit will be noted that the line Si is connected to the left hand end of acylinder 94 con taining a piston 95 which is normally biased to theposition shown in Fig. When the piston is moved to the right by theintermediate pressure established in line GI the stem 91 of said pistonengages and opens a normally closed valve 9' which controls th flow ofair line "connecting the prethe left hand end of the pilot valvecylinder I8 and'to operate the pilot valve 17 to the right therebyestablishing the connections necessary to operate the main control valveelement-,1 3 to its return stroke position. During the return stroke ofthe press the air supplied to cylinder 81 is exhaunted through the bleedvalve 12. 1 g

2 by the spring 98.x

I valve through which pressure fluid is routed Having thus describedwhat I now consider to be the preferred embodiment of this invention itwill be understood that various modifications may be resorted to withinthe scope and spirit of the appended claims.

Having thus described my invention, what I claim is:

1. A'hydraulic press including a maincontl'il} effect a working strokeof the press in one position of said valve and to efiect a return strokeof the press in another position of said valve, 2. collapsiblevalve-actuating toggle connected to said valve and serving, whenextended, to hold said valve in its first mentioned working strokeposition, a fluid pressure toggle-collapsing device comprising acylinder and a piston working in Said cylinder and connected to saidtoggle, biasing means arranged to shift said valve to the secandmentioned or return stroke position upon collapse of said toggle by saidpiston, a fluid line through which pressure fluid is conducted from saidvalve to the pressing cylinder of the press in the working 'str'oke'position of the valve, an

excess-pressure relief line connected to said first.

mentioned line at a point between the pressin cylinder and said valve, anormally closed working-pressure regulating valve arranged in saidrelief line and adapted to be instantly opened by the pressure fluidwhen the working pressure in the pressing cylinder is built up to apredetermined maximum value, said relief line and pressure regulatingvalve being of sufllcienig capacity to carry off from said firstmentioned linall the pressure fluid in excess of that required tomaintain the said predetermined maximum working pressure in saidpressing cylinder, 9. back presbe applied to the left hand end I thepilot valve to the sure regulating valve included in said relief line atthe discharge side of the working-pressure regulating valve andfunctioning, in the open position of said working-pressure regulatingvalve, to maintain a definite intermediate pressure in a portion of therelief line located between said valves, a valve-controlled fluidtransfer line connected between the cylinder of the toggle collapsingdevice and the portion of the relief line located between the dischargeside of the working-pressure regulating valve and the inlet side of theback pressure regulating valve and a valvecontrolled by-pass line havingone end connected to said fluid transfer line and the other endconnected to aid relief line at the discharge side of the back pressm-eregulating valve.

2. A hydraulic press at set forth in claim 1 including a variable strokehydraulic pump having its discharge side connected to said main controlvalve to supply pressure fluid to the pressing cylinder of the press inthe working stroke position of said valve, said pump being equipp d witha pressure responsive stroke adjusting mechanism and a pressure fluidline through which working fluid is supplied to and exhausted from saidmechanism, said line being equipped with a control valve and beingconnected between said stroke adjusting mechanism and the aforesaidvfluid transfer line through which fluid is supplied to and exhaustedfrom the cylinder of the toggle collapsing device. v

